The present invention relates to television signal processing. More particularly, the present invention relates to improved signal processing apparatus and methods for detecting motion picture film sources in television signals.
Portions of the present application are common to the copending application Ser. No. 08/948,539 of Yves C Faroudja, Peter D. Swartz and Jack C. Campbell entitled xe2x80x9cHigh-definition Television Signal Processing for Transmitting and Receiving a Television Signal in a Manner Compatible with the Present System,xe2x80x9d filed the same day as the present application.
In accordance with U.S. Pat. No. 4,876,976, it is known to detect that a 60 Hz NTSC television signal has as its source a 24 frame/second motion picture film. A 24 frame/second film is applied to and synchronized with 60 Hz NTSC video by using a 3-2 film pull-down ratio such that three video fields come from one film frame and the subsequent two video fields come from the next film frame (e.g., AABBBCCDDDEE, etc., where xe2x80x9cA,xe2x80x9d xe2x80x9cB,xe2x80x9d etc. are successive film frames). Video fields of the same parity in adjacent video frames are compared. When motion is present, a distinctive repeating pattern is obtained only if the video source is film (i.e., 1101111011, etc., where xe2x80x9c1xe2x80x9d indicates motion and xe2x80x9c0xe2x80x9d indicates no motion).
U.S. Pat. No. 4,982,280 discloses an arrangement for detecting a 30 Hz progressive scan source, which may be a video camera or film, in a 60 Hz progressively scanned non-interlaced television system. In the presence of motion from frame-to-frame within the 30 Hz progressively scanned video image sequences, when the video sequences in adjacent video fields are compared a 010101, etc. pattern results, indicating a 30 Hz progressively scanned source. Comparison of every second video field, to yield a 111111, etc., pattern, further confirms the 30 Hz progressive scan source. In order to operate, the arrangement relies on the spatial coincidence of pixels in the successive identical pairs of fields of the progressive scan television signal.
Published International Patent Application WO 94/30006 discloses apparatus for detecting twenty-five frame per second motion picture film sources in 50 Hz television signals, such as PAL, SECAM, 50 Hz NTSC, 50 Hz HDTV and 50 Hz monochrome television signals. The detection scheme looks for differences in motion between a field and the previous field, on one hand, and between the same field and the subsequent field, on the other hand.
The detection of motion picture film sources in television signals is useful in various environments, for example, a line doubler, a television standards converter, a television slow motion processor and a video information compressor.
A well-known xe2x80x9cline-doublingxe2x80x9d technique employs the conversion of an interlaced television signal (such as employed in the NTSC, PAL and SECAM systems), in which two time consecutive interleaved fields of scan lines represent a frame, to a non-interlaced or progressively scanned television signal, in which all of the scan lines in the frame are scanned out sequentially. The result, in the case of NTSC, is that 525 scan lines are presented every one-sixtieth of a second rather than 262.5 scan lines, thus potentially doubling the vertical resolution to the full frame resolution of 525 lines. Typically, line doublers employ, at least part of the time, field merging or inter-field interpolation, which provides a full doubling of the vertical resolution. Pairs of fields are combined to form a single progressively scanned frame. Such arrangements are described in U.S. Pat. Nos. 4,876,956; 4,967,271; 4,982,280; 4,989,090, 5,159,451 and 5,291,280.
One problem resulting from field merging is that there is a time difference between fields in the interlaced television signal. Thus, a moving object may be in different locations from field to field and, if two such fields are combined to form a single frame, the vertical and diagonal edges of objects moving horizontally or diagonally appear as ragged sawtooths rather than smooth curves. Line doubling is lost along such transitions. The sawtooth effect is exacerbated if the reproduction system employs vertical enhancement. A sawtooth pattern is an artifact created by the incorrect interleaving of two fields arising from different film frames. Visually what should be a continuous vertical or diagonal line will appear as a zigzag on the edge.
One solution to this problem is to employ some type of scan line or intra-field interpolation in regions of the television picture display in which movement is occurring. An improved technique for providing intra-field interpolation in areas of the picture having motion is set forth in said U.S. Pat. No. 4,989,090.
A potential problem with switchable inter-field/intra-field interpolation line doublers is that motion may not be properly detected at all times, thus allowing the above mentioned jagged vertical or diagonal transition artifacts to appear briefly and intermittently. Such arrangements may have particular difficulty in consistently switching correctly between operating regimes when operating on an interlaced television signal that has been subject to data compression or standards conversion (as from PAL to NTSC, for example).
Another known solution to the problem is to recognize when the source of the interlaced television signal is a motion picture film. As mentioned above, in the United States, 24 frame per second motion picture films are applied to the 30 frame per second NTSC television signal by means of a xe2x80x9c3-2 pulldown ratio,xe2x80x9d such that a patterned sequence of 3 film frames, 2 film frames, 3 film frames, etc. are carried by consecutive television fields. By identifying pairs of interlaced fields carrying the same film frame, the pairs may be merged to generate essentially perfect line doubled progressively scanned frames, each representing a motion picture frame. Such techniques are described in said U.S. Pat. Nos. 4,876,596, 4,982,280 and 5,291,280.
However, the motion picture film detection arrangement is also subject to problems. For example, a video edit (rather than a film edit) may disrupt the 3-2 pulldown ratio, causing merged television fields to be derived from different film frames. Thus, until the film pulldown ratio detection circuitry resynchronizes itself (typically one to four fields of the input interlaced television signal), the ragged sawtooth transition artifacts, described above, may appear at the edges of moving objects. Although the undesired effect is fleeting, it is perceptible to the eye, occasionally disturbing an otherwise near perfect line doubling arrangement.
The last discussed problem may also arise in the motion picture film source line doubling arrangement when the input interlaced television signal fades from a film source to a video source. In that case, the system, as described, for example, in said U.S. Pat. No. 4,982,280, continues to operate in its xe2x80x9cfilm modexe2x80x9d for a few fields before recognizing the loss of the 3-2 pull down pattern and switching to an inter field/intra-field interpolation arrangement of the sort described above. During those few fields before changeover from the film mode of operation, the same sort of ragged sawtooth artifacts may be generated if there is motion between the fields. In addition, the problem may also arise when the interlaced television signal derived from a motion picture source has been imperfectly data compressed or standards converted.
One solution to the problem of video edits disrupting the 3-2 pulldown ratio is set forth in said U.S. Pat. No. 5,291,280. The solution employs a field motion detector and includes circuitry to xe2x80x9clook aheadxe2x80x9d for video edits. However, as is explained in connection with the various aspects of the present invention, there are shortcomings in said U.S. Pat. No. 5,291,280 and in other prior art such that there is still a need to provide a better film motion detector for use in line doublers and in other applications as mentioned above.
The present invention has a number of aspectsxe2x80x94an improved field motion detector which does not treat low frequency vertical transitions as motion; a frame motion detector having an improved ability to differentiate motion from subcarrier signal components; a sawtooth artifact detector; a sawtooth artifact detector in combination with a film pattern detector, such that the artifact detector can take the film pattern detector out of film mode earlier than it would if it only were responsive to a break in the film pattern; tandem field motion detectors; an improved field based film detector; film pattern detectors and motion detectors used therewith which operate by performing end-of-field calculations; the combination of a field motion detector and a frame motion detector such that the frame motion detector provides a motion signal used as a verification by the field motion detector; an improved NTSC film detector requiring a minimum number of NTSC film pattern sequences; an improved PAL film detector employing a minimum motion threshold detector; combinations of these various aspects; and a line doubler (interlaced to progressive scan converter) incorporating one or more of these various aspects.